Engineering topics

Lee, J.-J.

Publications and source records attributed to Lee, J.-J..

3 records

NASA NTRS1979

Block adaptive rate controlled image data compression

A block adaptive rate controlled (BARC) image data compression algorithm is described. It is noted that in the algorithm's principal rate controlled mode, image lines can be coded at selected rates by combining practical universal noiseless coding techniques with block adaptive adjustments in linear quantization. Compression of any source data at chosen rates of 3.0 bits/sample and above can be expected to yield visual image quality with imperceptible degradation. Exact reconstruction will be obtained if the one-dimensional difference entropy is below the selected compression rate. It is noted that the compressor can also be operated as a floating rate noiseless coder by simply not altering the input data quantization. Here, the universal noiseless coder ensures that the code rate is always close to the entropy. Application of BARC image data compression to the Galileo orbiter mission of Jupiter is considered.

Rice, R. F.↗

NASA NTRS1976

Evaluating the GPSS simulation model for the Viking batch computer system

In anticipation of extremely heavy loading requirements by the Viking mission during the post-landing periods, a GPSS model has been developed for the purpose of simulating these requirements on the Viking batch computer system. This paper presents the effort pursued in evaluating such a model and results thereby obtained. The evaluation effort consists of selecting the evaluation approach, collecting actual test run data, making comparisons and deriving conclusions.

Lee, J.-J.↗

NASA NTRS1974

Families of shift-register sequences with impulsive correlation properties

A study of the linear feedback shift registers corresponding to a subset of nonprimitive irreducible polynomials over GF(2) has uncovered a class of sequences with interesting structures and cyclic correlation properties. These families of sequences are made up of interleaved identical sequences which are from primitive irreducible polynomials. Furthermore, they have correlation functions which are two or three valued, being constant at zero or a small value throughout most of their length with the exception of a small number of impulses. Each interval between such impulses on the correlograms uniquely corresponds to (and thus uniquely identifies) the member sequence or sequences producing it. It is shown that these families of sequences have direct application as error-correcting codes.

Lee, J.-J.↗